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Why changes the lift during turning with sidewinds? Why is there relative wind in the wind-frame?
I started doing some simulations with XPlane and could observe a very interesting effect when doing turns in the presence of constant wind:
All simulations are done with the XPlane Cessna 172 (?) with the motor turned off in gliding. (I want to simulate an emergency approach)
I control my plane to have a constant glide path angle and a constant roll angle. No coordinated turn. When I do so without wind, I get perfect circles with a true airspeed (TAS) that is decreasing with decreasing elevation. My glide angle controller has not too much work to keep the gliding angle perfectly constant.
However, if I turn on some constant wind, I can observe,

firstly: my circles change to trochoids over ground
secondly: my glide angle controller needs to counteract depending on the relative heading to the wind. When I am in a sidewind situation where the wind attacks the outer (higher) wing, the true airspeed is decreasing and when after a half circle the wind attacks the inner, lowered wing, the true airspeed needs to be increased to hold the gliding angle. In the quarters of turning with straight headwind or tailwind, the true airspeed is equal. So this results in a sine-like true airspeed profile with respect to the actual turning heading.

So in principle, I can imagine, that wind attacking the higher wing increases lift as it raises the whole plane from below and when it attacks on the lowered wing, it pushes the whole plane down from above.
What I don't really understand is why I experience this relative sidewind at all? My plane flies trochoids over ground instead of circles, as the wind blows the whole wind frame away. But shouldn't be the windframe kind of windless with regards to the plane?
My naive idea was, that the whole plane with its own wind frame is moved constantly by the wind, and calculating true airspeed within this wind frame is the same as in the no-wind condition. (see e. g. https://aviation.stackexchange.com/a/26332/30632)
Where do I over-simplify?

How does your glide path angle controller work, and how do you calculate the glide path angle and target glide path angle?

Holding "constant glide path angle and a constant roll angle" does not use any ground reference (except the horizontal plane reference). If the wind is constant, there should be no difference; the airplane will simply move with the wind. But if you measure "glide path angle" with respect to ground, and try to control pitch to hold it (not a very wise idea for gliding), then you should see the biggest difference in up/downwind segments and none in crosswind. Something is wrong there. What exactly do you control?

I use the X-Plane dataref named "sim/flightmodel/position/vpath" which is described as "The pitch the aircraft actually flies. (vpath+alpha=theta)". So my assumption was, that this is exactly the tangens of true airspeed divided by the sink rate. However, when exactly analyzing my logdata, this is again only true for the straight flight and not for turning in the wind. When turning in the wind, I see again some oscillations in the difference of the vpath dataref and the angle calculated from TAS and sink rate. I have to investigate that further.

Wind cannot 'attack' your wing, because there is no wind relative to your aircraft, only relative to the ground.  You are flying in still air; the still air in which you are flying is moving over the ground.
Your path over the ground is affected by the wind, so your first bullet point is correct.  'Wind' (in the weather sense) is the parcel of air in which you are flying, moving relative to the ground.
In your second bullet point, if your speed is varying, it must be due to a change in the controls, resulting in a pitch attitude change, or a change in power setting.  I'm not sure what you mean by "glide angle controller" but that would usually be the pilot.  Your speed cannot vary as a result of the wind, as there is no wind relative to the aircraft.  Only by referencing an external frame of reference (looking at the ground, looking at GPS) can you tell that there is any wind.
So if you are experiencing any sidewind (or any other wind), it is caused by whatever is controlling the aircraft (pilot or something in the program) referencing something other than the air.  This experience cannot be caused by a constant wind.

Thanks for the explanation! Meanwhile, I found out, that this strange effect was caused by the use of  "sim/flightmodel/position/vpath" which is described as "The pitch the aircraft actually flies. (vpath+alpha=theta)" in X-Plane. This vpath is obviously not correctly described, but is is the angle resulting from the forward ground speed of the airplane divided by the sink rate.
When changing my controller to control the angle resulting from TAS divided by sink rate and keeping this constant, this effect does not occur which is totally in line with your explanation.


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Why not stream outside cameras into the in flight entertainment system
Why do some carriers choose not to stream external views on planes where GMCS cameras are standard, such as the 777-300 or the Airbus A380?

I can't find it, but there was a crash that the passengers got a "birds eye view" of while they crashed. I thought it was American Flight 191 but I'm not sure. 191 had a "cockpit" camera that showed the pilots to screens in the cabin, so they may have watched the pilots struggle first hand.

I do not think this contributed to the crash

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Why don't the contrails show the curvature of the Earth?
When we see contrails in the sky, let's say traveling left/right in your vision, you are seeing across a sky that is easily a couple of hundred miles wide. I mean, we can see one side of space and then another, so we can see across a great distance in the sky depending on the height of an object.  Am I wrong?  I mean, we can see entire cities from a long distance away on the ground, so an unobstructed view of the sky would give us the ability to see something very long, right?
That being said, an airplane is following a curve, and when a plane makes a trail it is essentially tracing out the shape of the earth. Being that this trail is very high up, and following the curve, why don't the trails curve (left/right trail), and we see a giant arch across the sky?  None of the lines in the sky look curved from any direction, they are straight lines, or at least appear to be.
Am I missing something?  Maybe it's a dumb question, but I remain ignorant on the topic because I haven't been able to find the answer from anyone with a clue.  This site seems legit, so I asked it here.  Thanks, in advance.

See this link the second answer from the top.
Basically the answer is the curvature of the earth is too small to detect by the naked eye.  From a point on the earth, the observed point on the horizon will only drop by 8 inches for every mile.  This is why there are flat-earthers because they say they cannot see the curvature of the earth.  Airplanes don't exactly fly in exact straight lines either and you cannot see the slight variations in flight path from the naked eye that far away.

But, boats are going over a curve and you can see that with the naked eye.  You can see the bottoms of building be cut off, which is supposed to happen because of the curve.  That isn't far away.  If the curve is that close, then why shouldn't you see this represented across several hundred miles up in the sky?  I get how we couldn't see it on the ground, but the lines in the sky represent the shape of the earth, as if it's being traced. I don't understand how you couldn't see an arch spanning across several hundred miles in the sky.  Again, maybe that is ignorant, so my bad.

The cases you described are where you are looking horizontally a building and ships that are tall compared with their surroundings and with a completely flat horizon.  Contrails are vertical from your observation point.  Your depth perception cannot discern a curve that subtle.

@Chris when you take plank, rise it to your eyes and look along it, it's very easy to say it's warped even by a single mm. But when you look at a even more warped plank from the side, it looks "straight enough". Looking along a horizon from a ship vs looking at a contrail up there is same thing.

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How long have commercial aircraft been continuously in the sky?
In 2018, it's obvious that at any moment of the day, there is at least one (and in fact many) commercial aircraft in the sky. In 1908, this was not true.
Which was the last year there might have been a moment with no commercial aircraft in the sky? Please argue for your estimated year.

The definition of "commercial" aircraft may not have remained clear during the total mobilizations in WW2.  Depending on what your criteria for commercial is, WW2 could end up being the dividing line just because of that.

This is a great question and I will try to answer as I think it was intended. Based on reasonable assumptions, I can estimate that at least one commercial passenger flight has been in the air somewhere in the world continuously since the early 1930s.
A key help in answering the question is that passenger aviation grew very rapidly throughout the mid-20th century. Moreover, the chance probability of having zero flights in the air at some moment is mathematically very sensitive to the overall rate of flights. Thus, the historical window in which an "empty sky" is plausible would close quickly. Past some point, the overwhelming growth makes it virtually impossible that the skies would ever be devoid of commercial flights again, unless some event stopped them in sync almost everywhere in the world.
What about World War II?
In North America, despite the diversion of a significant fraction of people and resources to the war effort, many commercial passenger flights continued. Schedules in the early 1940s showed numerous routes operating at all hours of the day and night. So much growth had occurred in the 1930s that even the dent from the war left the industry well ahead. (This may well have also occurred in Australia, another developed region mostly spared the direct violence of the war domestically.)
What about 9/11?
Although US and Canadian airspace was closed after the attacks, flights continued within the rest of the world -- again making a dent but not undoing decades of growth.
So why the early 1930s?
Due to the aforementioned rapid growth, we will be pretty close if we merely get the orders of magnitude right. Assume a typical flight length of 2 hours or 200 miles in this era. Also assume that flights were uniformly distributed over a time period (say a year) -- equally likely to be scheduled at any time 24/7/365. Even within one region, flights operated day and night, and superimposing the various global time zones (even just North America and Europe) further homogenizes the flight schedules.
If we can estimate the average number M of commercial flights in the air at any moment, we can model the fluctuations statistically as a Poisson distribution. According to the Poisson distribution, the probability of finding zero flights at a given moment is e^(-M), where e ~ 2.7. This result is fairly robust; for example, if we take a different model where there are 2*M planes in the global airline fleet, each of which is flying half the time (thus M are in the air on average), then the chance that no plane is flying at a given moment is (1/2)^(2*M) = 4^(-M). The key result is that the probability decreases exponentially with M.
Roughly every 2 hours, the flights "turn over" (current flights have landed and a new set has taken off), giving us a new sample from the probability distribution. During a year, we get about 4,000 samples, and the probability that we see zero flights at least once is roughly 4,000 * e^(-M). Of course, M is increasing from one year to the next as the industry grows. We conclude that once M surpasses about 15, the probability of ever again having the sky globally devoid of commercial flights is negligible.
In the year 1930, there was already a noticeable passenger airline industry in the US (at least 6,000 passengers flown, which is likely very low because another source says over 300,000) and in Europe (10,000 in Italy, 18,000 in the Netherlands, not to mention the UK, France, and Germany).
If we estimate a worldwide total of >100,000 passengers for the year, and consider that a typical ticket was for several flight segments, say 1,000 miles, then we get >100 million passenger-miles in 1930. As further confirmation, the US alone is quoted at 84 million passenger-miles that year.
The planes were very small and load factors were low, so the typical number of passengers on board was likely around 3. Thus, passenger flights worldwide traveled at least tens of millions of miles in 1930 (compare 37 million revenue miles for US airlines, which may however include some cargo flights without passengers).
At an effective speed of 100 miles per hour, the total flight time was at least hundreds of thousands of hours. With the year containing about 9,000 hours, the sought average number M of planes in the air at once would be dozens. By the statistical reasoning given previously, this is the point at which the "empty sky" probability becomes negligible. And if we are off by say a factor of 2 in estimating M (e.g., due to seasonal variations), this corresponds to just a few years of growth.

This depends very much on your area of interest. It might be difficult to find a global answer, but it's certainly possible to find answers pertaining to parts of the world.
Apparently, very large portions of China's airspace is open only to the military. So for huge swathes of sky there, it's likely that there are no commercial flights even today.
U.S. airspace was shut down at least to international flights on September 11, 2001. So that'd probably be pretty close to an answer for the U.S.
Wikipedia claims that over two dozen European countries had airspace restrictions following the 2010 Eyjafjallajökull eruptions in April of that year. My understanding is that these airspace restrictions affected jet aircraft only; piston-propeller aircraft were allowed to fly, and though I'm not sure about turboprops, I'd hazard a guess that those too were grounded as many of the issues with volcanic ash ingestion into jet engines would seem to apply to turboprops as well.

I think they're asking globally, but I might be wrong.

@Federico Yeah; I'm not sure. If this is a bad answer, I'll delete it. But it seems establishing when this has happened in some part of the world is at least a partial answer to when it has happened everywhere in the world.

After 9/11, ALL US flights were grounded for a day or two. A lot of companies scrambled to rent vans and such to get employess home from trips around the country.  I went flying on 9/15, but had to file IFR and take a bit of a zig-zag route while Boston Air Traffic Control picked me up on radar.  On a side note: Scientists took advantage of the lack of contrails over the southwest US skies to see if any change in temperature could be observed.  I recall yes, but I don't recall if it was an increase or decrease.

@CrossRoads - The study was for diurnal temperature range, the difference between the high and low temperature for the day.  A few years later the findings were challenged by a follow-on study.

I wonder why it someone 8 years to challenge it?

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What is this fighter jet seen at Centennial Airport?
This is my first post here! yay! Today I ate at the awesome "Perfect Landing" restaurant at Centennial Airport. My dad said he thought they were FA-18s but I honestly have no idea. It was awesome because we saw the pilots through the window of the flight crew lounge in their military suits. We also saw them go out with some little kids and their families to show them the jets while they were being inspected before takeoff. Really cool to see.

That is a Boeing F/A-18E Super Hornet.  The Super Hornet can be readily identified from legacy F-18s by its larger size, enlarged, hood-like leading edge extensions, larger flaps and flight control surfaces, and the rhombohedral shaped engine intakes to reduce the aircraft’s frontal radar cross section.  It’s tail insignia indicates that it’s a line aircraft with the United States Navy’s VFA-143 “Pukin’ Dogs” strike fighter squadron based out of NAS Oceania, near Norfolk, VA.

It’s a unit specific tail code.  All VFA-143 aircraft wear the AG code on the tail.  https://en.m.wikipedia.org/wiki/U.S._Navy_and_U.S._Marine_Corps_Aircraft_Tail_Codes

Wow I can’t believe how much information you can tell me from 1 picture! That’s really cool and now I know some awesome information about the squadron itself. There were 3 of these jets here.

Wow - “rhombohedral shaped”- after I look that up, I am definitely going to have to find a way to use that phrase in a conversation this week!  +1

That's a very complete answer. Well done.

@Sorsor_7 not sure if this is still the case, but also used to be A codes were for wings on the Atlantic coast and N codes for the Pacific coast (both Navy wings, USMC uses different conventions).

"It’s a unit specific tail code. All VFA-143 aircraft wear the AG code on the tail."  Technically true at the time the photo was taken, but potentially misleading.  The "unit" in this case is the carrier airwing, not the squadron.  If the squadron were to be reassigned, as often happens, it would sport new tail letters to match all the other squadrons in the wing.


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Does the required torque to spin a propeller increase with RPM?
I‘ve currently been experimenting with different propellers: 12x12 prop, 16x12 prop (both two blades) and a 22x14 (6 blades) prop. They were propelled by a 2.4 kW electric motor with 260 kV on a 6S/5200mAh/12C battery setup.
The 12x12 prop produced 2 kg of thrust at full throttle, the 16x12 produced 4.5 kg of thrust. So I thought the 22x14 would produce around 6 kg because its bigger blade area would be more efficient. However, I got only 0.8 kg of thrust and recognized that the motor would slow down at a certain RPM.
I have to say the big prop is pretty heavy so could it be that the motor would have enough power to spin the prop faster but it lacks enough torque to get it there?

"could it be that the motor would have enough power to spin the prop faster but it lacks enough torque to get it there ?" - I don't think power and torque are separate like that. Failure to produce enough power is failure to produce enough torque, and failure to produce enough torque is failure to produce enough power. Though it is true that the maximum power output of a motor depends on the torque.

@TannerSwett: At any given speed of rotation, power and torque are proportional, but the proportionality is different at different speeds. Motors are generally torque limited at low speed (they can produce plenty of torque but not much effective power) and power limited at high speeds (i.e. delivering maximal power at only a fraction of the torque they can reach at low speed). The behavior in between depends on the details of the engine.

Yes the required torque increases with RPM. With simple impulse theory, the torque Q on a rotor or propeller is:
$$Q = C_Q \cdot \rho \cdot A \cdot \Omega^2 \cdot R^3$$
Where $\Omega$ is the angular velocity = RPM. So the torque required goes up with the square of RPM, and since power = $Q \cdot \Omega$, the power increases with RPM$^3$. All other factors remaining as they were of course.
That is simple impulse theory however, which does not consider disk solidity and blade profile drag. For a given thrust and blade radius, torque and power increase with number of blades since there is more blade profile drag to overcome.

Mechanical power is always the product of an effort (torque) times a flow (RPM) variable. Similarly, electrical power is always the product of an effort (voltage) times a flow (current) variable.
The design problem of optimizing a motor-and-propeller combination for maximum power then always boils down to this: 1) determining the RPM at which the motor produces peak power (torque x RPM), 2) knowing the voltage and current required to produce that power, and 3) specifying the propeller which can absorb that amount of power at that specific RPM.
The analysis is complicated by the fact that from a dynamical systems modeling standpoint, a DC motor is a gyrator, in which the input effort variable (voltage) is proportional to the output flow variable (RPM).

I added a link to the Wikipedia article for "gyrator," because I had never heard the term before.  Although after reading the article, I can't say I really understand it any better.

Firstly, take the six blade and throw it away.  2 blades are best until the arc hits the ground in front of your plane, then go with 3.  Curious as to the application here, is it a microlight?  Might help also to consider pitch too, but you are definitely on the right track with the 16x12.
If I am not mistaken, it is longer than the 12x12 with the same pitch.  You can get a rpm measuring device from a hobby shop to measure peak rpms, but as you are already measuring thrust it is not absolutely needed.  Now you can try 15x12, 17x12, maybe 18x10
(longer with less pitch) until you get it perfect.  Pitch is just like gears on a car, lower means better acceleration from standstill and better at climbing, higher will give lower rpms at cruising.  I would keep trying, and make sure the battery/engine can handle the load without
going up in flames.  Definitely check with an expert as you have some serious prop there.

Thanks for your answer. I know that 2 blades are usually most efficient. However, the purpose of this project is to maximize the thrust per area so 6 or even 12 blades should be better here. My problem was that with the 6 blade 20 inch prop I got like a third of the thrust of the 12 inch prop with the same motor. Now I know it´s because of the higher torque requirement of the bigger prop.

OK.  This is a great one to continue for three reasons. First, we are also seeing blade turbulence interference on the 6 blade compared with 2.  Second, because of 12 pitch, you are probably spinning stalled blades.  Third, seeing maximum load on your battery/motor, which you can monitor a watt meter.  So maybe get a 10 inch 6 blader with pitch range of 4 to 12 (several of them).  Notice this all changes once the plane is moving.  With a 150 mph headwind, higher pitch is better.  With static bench testing, the AOA is more, just like a wing.  This is why variable pitch props were developed.

So, not to spoil the ending, after safely continuing with smaller blades, you will find, just like with jets, you get more thrust per area by increasing power of engine and adding blades, at the expense of efficiency.  Jets have more thrust, but are not as fuel efficient as piston engines with 2 blade props.  But they are much faster indeed.

So after you pick your prop diameter limit, spin a low pitch 2 blader right up near the speed of sound. That is your RPM limit.  Then try pitch for max thrust, that is your best AOA.  If RPM is not dropping yet, motor has more to give.  Widen the 2 blade or move to 3 blade.  Very cool experiment.  Might be good to approach from small/fast side.  Don't think you will go past 4 or 5 blades, I could be wrong!

Ok, what would you suggest as a limit for blade tip speed ? Mach 0.6 ?

A 12 inch prop spinning at 20,000 rpm:  1 foot x 3.14 x 20,000 r/min x 1 mile/5280 foot x 60 min/hour = 713 mph tip speed.  A powerful electric motor can do this.  As we are testing for thrust, and as "lift" from prop will be the square of its speed, I suggest to start with 2 blades, lower AOA(around 6 pitch), and fast, with mach 1 as the limit.  As a technician, I would thoroughly enjoy adding experimental data to go with the theory (but being careful to avoid prop arc)

If the other factors remain constant, the torque required to rotate a propellor will increase with RPM. The power requirement is a function of torque and RPM.


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What is the reasoning behind Kamov twin-rudder design?
Several helicopters, namely the Ka-226, the Ka-25, and the Ka-27, have twin vertical stabilizers that are canted inwards at an angle of about 15 degrees, similar to the feathers on a shuttlecock.
The stated purpose of this design is to increase directional stability during auto-rotation, but I cannot find any information as to why the inwards angle is used in general, and more specifically, why it seems only these models of helicopter need them.
My best guess is that much like the shuttlecock, when in straight flight, both stabilizers will have a positive Angle of attack and will be generating inwards lift, which is a more stable condition for low forward speeds.

It's kind of a hard one. It looks like in this helicopter directional stability is a challenge because:

the tail arm is quite short;
there is no tail rotor, which provides directional stability just like a vertical tail does.

An aerodynamic surface is most effective around zero angle of attack of the air stream - slipstream angle $ \beta $ in this case. Most profiles stall at angles around 15 degrees, and are therefore most effective at -15º < $ \beta $ < 15º.
If we have a look at lift L and drag D of the vertical surfaces, with dynamic pressure q in N/$m^2$, A = total vertical tail area in $m^2$, and $C_L$ and $C_D$ dimensionless coefficients:
$$ L = C_L * q * A$$
$$ D = C_D * q * A$$

The two images above are from Principles of Helicopter Aerodynamics by J. Gordon Leishman Figure 7.51. They show the coefficients over a full range of 360 degree, and we can see that:

In the $C_L$ plot, after the stall point at about 15º there is still quite some lift left, that increases again but to a lower peak at about 45º according to flat plate lift theory. That means that between 15º and 45º, there is not much increase/decrease in lift: $dC_L/d\alpha$ is almost zero and the surface is very ineffective in stabilising in this range. There is even a little dip in the curve just after the stall where the angle might get stuck.
In the $C_D$ plot, there is a deadband between -15º and 15º, after which the drag jumps up dramatically and has a relatively high $dC_D/d\alpha$. Since drag is defined as the force in line of the air stream, at higher angles of attack drag actually helps in getting the surface back to neutral (At 90º lift is zero and all force is drag)

So with the above in mind, what it looks like to me is that due to the short tail arm the vertical surfaces must deal with helicopter slipstream angles > 15º. By canting them inwards, one surface operates in the effective $C_L$ range, and the other surface operates outside the $C_D$ deadband, in doing so channeling the drag forces into a stabilising moment. And as @PeterKāmpf mentions in a comment, the high-drag rudder has a high moment arm, which makes it more effective.

Right, and the high-drag rudder is way out to the side, so it's drag has a high lever arm. BTW, rudders with such a low aspect ratio will easily work until ±20 or ±25 degree AoA, but the principle still holds true.

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What is this 'ball' in front of the cockpit of some fighters, e.g., an Su-57?
What is the lump/ball thing visible below and to the left of the canopy in this image of a PAK FA (which became the Sukhoi Su-57), and what is it for? It's also seen on other fighters.

Image source

That is the infrared search and track (IRST). This particular model of an IRST is known as the OLS-50M in Russia and uses quantum well photodetectors.
Radar has two serious limitations, one is that advanced software can jam it, the other is that you give away your position when transmitting radar signals.
An infra-red sensor can be used to find and destroy targets without giving away the position of the aircraft and cannot be jammed. IRST is especially effective at detecting low-flying vehicles like helicopters that would otherwise be lost against a background. IRST can also be used to find, hunt down and kill ground vehicles.

Being on top of the plane I doubt it would be very useful to detecting vehicles under you or on the ground.

@Michael The Russians fly inverted when they want to collect a ground target with the IRST.

@Michael being where it is on most aircraft (infront of the cockpit, directly behind the nose) you would be surprised just what it can pick up, especially as those noses are built to be transparent in a lot of wavelengths, so in most IRST systems they don't block its view.

@Moo it's optical. Means it cannot see through opaque surfaces. And when it works, its lid is open.

@Abyx its not optical, its infrared, and lots of things can be made transparent to infrared but opaque to visual wave lengths.

It's called "Infrared light" for a reason; and there's no way that nose radome is transparent to any frequency of light.  It may be translucent in some frequencies, but that's not going to help here.

@Riot, visible, infrared, ultraviolet, X rays, γ radiation, they are all "light" in a sense. They are electromagnetic waves. I guess the term "light" may be more frequently used for the visible and nearby frequencies but I don't think that referring to X-rays as light for example is wrong. No more than referring to infrared as light. So when you say "any frequency of light", what frequencies exactly are you referring to?

quantum well photodetectors !

That is an passive Infra Red Search and Track (IRST) sensor.  Used to passively identify and track aircraft using their emitted infrared energy.  The system pictured above is used solely for an air-to-air role and does not have a use for identifying and tracking ground targets.

I can't speak to the use of the OLS-50M specifically on the PAK-FA, but the description page for it does say that it's used for air, ground, and water targets. It was developed for the Su-35, and on that craft it's in the exact same position, leading one to believe that it's capable of detecting ground and water targets on the T-50 as well.


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Why does the Ka-50 (Hokum) have coaxial rotors?
Why does the Kamov Ka-50 Black Shark have two coaxial rotors? Is this a better design than a conventional one rotor?

Please do a little basic research before asking here. In this case, your question is already answered by the Wikipedia article about this particular helicopter. If there's something you don't understand in the explanation there, ask a question about that.

@DavidRicherby If we refused to answer questions that already have a relevant Wikipedia article, this site would be a lot smaller :-) The community consensus so far is that we should answer as many questions as possible, even if answers are already available elsewhere. Having said that, I do agree with you that people who do some research first usually ask better questions.

I agree with @Pondlife It's a perfectly valid question: Why does a helicopter have two stacked rotors instead of one? P.S., some people don't trust Wikipedia. Another possibility is that newbies don't understand what the wiki is trying to explain, especially a relevant term like "coaxial rotors".

The ka-50, like other coaxial rotor designs, use their contra-spinning rotors to cancel out the torque in the same way a traditional helicopter uses it's tail rotor.
A traditional single rotor:

Source
Contra-rotating rotors:

Source
There are a few benefits of the contra-rotating setup, such as

Reduced vibration
Reduced likelihood of settling with power
Reduced likelihood of anti-torque failure during flight.

@KorvinStarmast The term is quite complicated, but luckily there is a question that addresses what it is.

@KorvinStarmast I specifically linked that phrase to the canonical question right here, because I guessed it may not be a familiar term.

poor question, but +1 for the mesmerizing gif!

And I always thought that the biggest benefit of using coaxial rotors is dynamic stability.

I'll add another point to the Jamiec's answer, which particularly applies to Ka-50.
A coaxial helicopter is almost symmetric, and it is much easier to fly it. This is largely why they dared to create a single-seat combat helicopter in the first place: the pilot could fly it (at a low altitude!) and still have enough attention span for weaponry.
It is also astonishingly manoeuvrable, particularly in yaw (with respect to comparable classic designs). A classic helicopter would need an oversized tail prop to achieve the same angular speed (at least in one direction), which would be a hindrance for normal flying. The gun turret on Ka-50 has very limited horizontal (left and right) aiming range, which is used only for automatic aiming adjustments. This is because it is easier to aim the whole helicopter, even when it's flying with a substantial speed.


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What is the operating temperarature of a scram jet at its theoretical maximum speed?
What is the operating temperature of a scram jet at its theoretical maximum speed of Mach 24?
For those with access to a simulator and do such simulators exist and are they possible?
Given this speed is achievable and there are no known existing materials that can handle the temperatures, would ceramic shielding along with liquid cooling assisted by refrigeration technology suffice and is it feasible for both the engine and air frame?

Could you add a link or and explanation how the maximum speed is calculated? Is this based on the orbital speed? Given that the speed of sound varies with altitude (as does the orbital speed?!) the Mach number changes with altitude as well. Or is there another fluid-dynamics limit?

The most efficient operating altittude for a scramjet

ok, so let's say we would know the most efficient altitude, how do we calculate the theoretical maximum speed?

between 70 and 75 km altitude maximum and Mach 24 maximum speed using hydrogen as fuel


text:
What is the call sign for the US president's private helicopter?
The Air Force VC-25's are Air Force One, Marine aircraft are Marine 1, a private jet is Executive 1. What about when the president is using one a private helicopter?

OH man... so many names come to mind... LOL most them would be deleted here....

The callsign of a civil aircraft transporting the President of the USA is Executive One, as you already mentioned yourself. An aircraft owned by a corporation which happens to share the name of the president is not any different. (According to a comment by Dan Sheppard, Vice President Nelson Rockefeller used his personal plane, whose callsign was Executive Two – this would be the closest thing to the situation you ask about that has actually happened.)
However, as was already mentioned in another answer, it is highly unlikely in this day and age that the Secret Service would allow transporting the President on anything other than one of the VC-25s, VH-60Ns, SH-3s, or "The Beast", publicity stunts such as George W. Bushs flight with the Lockheed US-3A notwithstanding. Note that this was the only time so far that the callsign Navy One was used, which tells you something about how often something like this (POTUS using an aircraft other than one of the VC-25s, VH-60Ns, or SH-3s) happens.

Vanity Fair says that POTUS is not allowed to use his private helicopters due to safety protocols.
They will not have any special callsign when flying (since he won't be aboard), and they would most likely use their tail number, or something mundane like "Trump 1" and "Trump 2".


text:
Why did my phone's GPS receiver stop working when the plane was descending to land?
Recently, I flew on an Airbus A320. I turned my Lenovo A328 Android phone into airplane mode, and then used the default Maps app to watch my position using GPS. For most of the flight it worked normally. However, at the end of the flight, at about the time the plane started to descend so as to land, the GPS position marker suddenly jumped to an obviously wrong spot. After that, it ceased to update — at least until I got out of the plane.
Is it expected behavior of a phone GPS receiver during a flight? If so, what causes it?
It seems the plane does need GPS itself to be able to, e.g., send ADS-B data, so it doesn't seem likely that it jammed the signal. It also doesn't look like the clouds could be an obstacle for GPS signals, since after the landing the operation of my phone GPS receiver resumed (being under the clouds).
For reference, here's flightradar24 data about my flight.

Cloud is an obstacle. Cloud plus the fuselage could be the difference between a good enough reception and none.

@Antzi I'm fairly sure that clouds don't block GPS signals, do you have some reference for that?

@Pondlife: And you are right, even if this attenuation graph is for water vapor (which is invisible)  and not water droplets. However leaves attenuate significantly the signals.

A GPS needs a line of sight to (at least) 4 satellites in order to compute a position. Given that you were able to get a position during the cruise, I assume that you were close to a window and had a clear view of a part of the sky.
During the cruise, the aircraft trajectory was close to a straight line (or changing slowly), so your receiver was able to keep a line of sight to the same set of satellites. But during the approach, the trajectory was much more dynamic (lots of turns), so your receiver didn't had a constant line of sight toward the same set of satellites and "lost" them. It takes time for a receiver to "lock" on the signal of a given satellite, so the receiver it couldn't compute a position from other satellites because they were not in sight long enough.

This seems to be a reasonable explanation.

Add to that the fact that larger planes seem to possess Faraday cage-like qualities; all commercial flights I've flown on recently only gave me very poor, borderline GPS reception. Pressing the phone against the inner window made a big enough difference that if I moved it half an inch away, I'd lose signal. High speed trains seem to exhibit similar characteristics. Phone GPS chips being deafened by local RF sources?

@ChristopherWoods GPS chips being deafened by local RF sources ? I don't think so, if it were true then cell phone would also be jammed.

I would also consider tha the fuselage will block all satellites except the ones near the horizon. As you start to descend those will disappear over the horizon

@ChristopherWoods, the GPS L1 band (the one interesting to civilian receivers) is 190 mm wavelength and that only barely passes the window, with a lot of diffraction and attenuation. There is no local noise on the band; it is really mainly the shielding.

The satlellites are constanly moving too, they are not stationary "GPS satellites fly in medium Earth orbit (MEO) at an altitude of approximately 20,200 km (12,550 miles). Each satellite circles the Earth twice a day. Expandable 24-Slot satellite constellation, as defined in the SPS Performance Standard." https://www.gps.gov/systems/gps/space/

If you get a good GPS APP you can see all the sats that are potentially known about, including those that are on other other GNSS (global navigation satellite service) services than GPS if your device supports it. The airplane body is a Faraday Cage, so is anything with a solid exterior metal skin. At the microwave frequencies GPS uses, even closely placed metalic dots can screen the signal that is why you can see into your microwave oven for instance without getting burned yourself. 1.9 GHz is not too far really from 2.4Ghz so the dots would only need to about 1/5 as close together.


text:
What are these aircraft at the Naval Air Weapons Station China Lake?
What are these 12 aircraft at the co-ordinates 35.677323, -117.676903?
I recognize the F-111 and C-130, but not the others.

Source: google maps

Are you asking about the Naval Air Weapons Station - China Lake?

There is no C-130 in the photo - I'm looking at the upper right as the suspect. A 130: (1) its fuselage does not taper in the back. (2) its fuselage is proportionally wider (3) its wing is high-mounted, it hides that part of the fuselage as seen from the top.(4) its engine nacelles are more streamlined, being a turbine. Those in the photo look like radial piston to me.

This answer is a Community Wiki.
Community edits are welcome.

The aircraft in the photo appear to be the following, or varients therof:

Douglas R4D-8 (Super DC-3)

source, photographer: Brian Lockett

North American T-39 Sabreliner
Boeing C-97 Stratofreighter or KC-97 tanker varient
McDonnell Douglas F-4 Phantom II

source, photographer: Brian Lockett

Vought F-8 Crusader
North American T-39 Sabreliner
North American RA-5C Vigilante tail number 156640

source, photographer: Brian Lockett

Boeing B-29 Superfortress

source, photographer: Brian Lockett

General Dynamics F-111B tail number 152715

source, photographer: Brian Lockett

Grumann A-6 Intruder
Douglas R4D-8 (Super DC-3)
Grumann A-6 Intruder

No C-130 appears in the photo included in the question, though one may appear elsewhere near the coordinates linked.
Notes:

1 and 11 are not C-47 Skytrain. They are longer and have a square tail which is typically for the Super DC3 / R4D-8
3 is longer from the wing root to the nose than the same measurement on 8, supporting that 3 is not a B-29.
Moreover, in the photo of 7,  aircraft 3 appears in the background which clearly shows engine nacelles like those of the B-50 or C-97 series.
The same photo shows a fuselage rising higher above the wing than a B-50, which is consistent with a C-97 variant.
5 measures nearer the 54 ft in length of an F-8, versus the 46 ft in length of an F-7, supporting that it is an F-8

3 looks more like the B-50 and 8 looks like the B-29

7 looks like a model of an early VFX/VFAX prototype; what would become the F-14. While swing-wing for speed and space, and dual-tail for maneuverability and stability, were both the vogue at the time, Grumman had designs for single-tail and fixed-wing variants of the VFX fighter carried forward from the doomed F-111B project.

10 and 12 are definitely A-6's by the way. You can make out the fixed probe on the left side of the cockpit, and the fuselage and strake lines are a dead giveaway.

@KeithS on bing maps it looks like it has one vertical stabilizer and I found a photo of the remains of an F 111B at China Lake. It seems to me that this is an 111B.

@KeithS you can edit this answer to add that info, if you would like

Good job on finding the ground photos

@DeltaLima - I actually don't think so. The F-111B was always going to be swing-wing like its Air Force counterpart, and the design also has leading-edge strakes over the top of the intakes and a fatter nose due to the side-by-side seating arrangement. Compare #7 to #9; that is absolutely 100% an F-111.

@KeithS Are you suggesting that 7 is an F-111? I think we have definitive evidence that 9 is an F-111B. I'm losing track of everyone's antecedents.

@KeithS In his book, California Warplanes, Harold Skaarup cites tail number 156640 (7 here) as an RA-5C.

@KeithS I now see your comment was related to no.7. Since you mentioned the F-111 I automatically thought you were talking about no. 9. Sorry for the confusion I created

1,11- Douglas C-47 Skytrain
2,6- North American Sabreliner
3,8 - B-29 Superfortress
4- McDonnel Douglas F-4 Phantom II
5- Vought A-7 Corsair II
7- North American Vigilante
9- General Dynamics F111 Aardvark
10,12- Grumman A-6 Intruder

1 and 11 are not C-47 Skytrain. They are longer and have a square tail which is typically for the Super DC3 or R4D-8

9 is an F-14 Tomcat. Note the single piece canopy vs. the Aardvark's split canopy, as well as the dual vertical stabilizers (the Aardvark only has one).

@SnakeDoc I only see one vertical stabilizer on 9. The intakes on 9 also do not match the F-14. I think this answer is correct on this being an F-111.

3 is not a B-29, but a B-50.

@SnakeDoc The aircraft is definitely an F-111. The Tomcat has very pronounced intakes where the wings meet the fuselage. The F-111 does not. If it were an F-14, you would see two "shoulders" for the intakes just behind the canopy. The F-111's intakes are underneath the wings, not in front like the Tomcat.

What is the B29 a plane of the Air Force and Army Aviation doing in Naval Air Weapons Station?

Confirm 7 is a North American A3J - A-5 - RA5 Vigilante. Looks a lot like a hot, 1960s fighter, a F-14, MiG-25, or F-15. I've read that Soviet espionage delivered enough A3J information that TsAGI based the MiG-25 shape on it. That's slightly odd, the A3J was a supersonic bomber with a deterrence role, like TSR-2. But Navy requirements included max weight catapult launches from an ANCHORED aircraft carrier. Deterrence means ready to go, 24/7. This was when the USAF had nuclear-armed bombers airborne, 24/7.

Douglas DC-3/C-47
North American T-39 SaberLiner
Boeing KC-97
McDonnell Douglas F-4
Vought F8U/RF8U Crusader
North American T-39 SaberLiner
North American A-5/RA-5 Vigilante
Either a Boeing B-29 or a B-50 Superfortress
General Dynamics F-111 Aardvark
Either a Grumman A-6 or a KA-6 Intruder.
Douglas DC-3/C-47
Either a Grumman A-6 or a KA-6 Intruder.


text:
What is this part between the Su-35's jet exhaust nozzles?
What is the long thing that sticks out between the Su-35's jet exhaust nozzles and what does it do?

Source: 4ever.eu

That's the stinger. The Su-35 will use it against an intruder if it's deemed a potential threat to the colony queen/aircraft carrier.

Are you sure it isn't an ovipositor?

The long thing has RWR (Radar warning Reciever) on its sides and has a drogue parachute in the middle. This image shows the rear part open after deployment.

Image from airplane-pictures.net
Incidentally, the aircraft serial number is 901, while the one in your image has a number 902.

Does the Radar warning Reciever do the same job that Hawker Siddeley Nimrod tails, with electronic warfare (ESM) sensors, do?

@Marine1 the Nimrods tail is a Magnetic Anomaly Detector, designed to detect a submerged submarine as the aircraft flies over it - its positioned in such a way because it has to be clear of the aircrafts magnetic field distortions.  The RWR on SU-35 and other aircraft merely detect when the aircraft is being hit by radar.

If you are speaking of the grey volume, according to this cutaway by Alexey Mikheyev, it contains a Radar Warning Receiver/Electronic Intelligence System. Basically a system designed to detect if an hostile weapon system is locking/has locked on you.

You have copied the cutaway from its source to Stack Exchange's imgur.com server. It would be best to provide attribution of the source for the image in your answer. In addition, if the cutaway has a license that makes it reasonable to put on Stack Exchange's imgur.com server to share in your Answer, then the answer would be better if you display the image in your answer rather than just link to it.

@Makyen I agree, but none of this was available. The image was on pinterest with no attributable source except the one in the top left corner of the image (that I left untouched). If you have found any linkable source I will be happy to include it.

Then it would be better to have the link in your question be to the source, rather than a copy.  Moving a copy to Stack Exchange's imgur.com server introduces copyright issues to your question. Having, instead, a link to the page where you found the image leaves the copyright issues on that site.

@Makyen but in turn not copying to imgur introduces the problem that the link might go dead.

That is one of the risks of complying with copyright. You can mitigate this risk by finding an archive of the site, or having an archiving site create an archive.

@Mayken we've discussed in chat. The outcome is that, as the author does not seem to have a website we can direct to, and his name is in the image, pointing to random 3rd party websites would not help him. I will report his name in the post.


text:
Was the F-4 Phantom the only fighter to be in service for the US Navy, Air Force and Marines?
As is stated here:

Furthermore, the F-4 came in both ground- and carrier-based models and
  served in the U.S. Air Force, Navy and Marines. The only other
  frontline fighter to serve in all three services before or since is
  the F-35.

Is that correct? Was any other fighter used by all three services?

As far as I can tell, it is accurate.

The statement is accurate.
Here is a list of all U.S. Fighter Aircraft, in service and retired on Wikipedia. The following is an excerpt from that list for relevant aircraft.

F-4 Phantom (Air Force/Navy/Marines)
F-5 Freedom Fighter (Navy)
F-6 Skyray (Navy/Marines)
F-7 Sea Dart (Navy)
F-8 Crusader (Navy)
F-9 Cougar (Navy)
F-10 Skynight (Navy/Marines)
F-11 Tiger (Navy)
F-12 Lockheed (Air Force, A12 Variant)
F-14 Tomcat (Navy)
F-15 Eagle/Strike Eagle (Air Force)
F-16 Fighting Falcon (Air Force)
F-17 Cobra (Air Force)
F-117 Nighthawk (Air Force)
F-18 Hornet/Super Hornet (Navy/Marines)
F-20 Tigershark (Prototype, cancelled)
F-21 Kfir C-2 (Navy)
F-22 Raptor (Air Force)
F-23 Black Widow II (Air Force, cancelled)
F-35 Lightning II (Navy/Marine Corps/Air Force)
F/P-80 Shooting Star (Air Force/Navy)
FH-1 Phantom (Navy/Marines)
F2H Banshee (Navy/Marines)
FJ-1 Fury (Navy/Marines)
F-86 Sabre/Super Sabre (Air Force)
F-82 Twin Mustang (USAF)
F7U Cutlass (Navy)
F-102 Delta Dagger (Air Force)
F-106 Delta Dart (Air Force)
F-104 Starfighter (Air Force)
F-101 Voodoo (Air Force)
F3H Demon (Navy)
FJ-2/FJ-3 Fury (Navy/Marines)
F-89 Scorpion (Air Force)
F-84 Thunderstreak (Air Force)

This list includes fighter aircraft introduced or in service after 1949, when the US Air Force was created until the end of 1960 when the F-4 Phantom came into service.
Table image was removed because the data is out-of-date. You can view the original image here.

Looks good to me, thanks.

Anything in the A series that would fit? The table is wrong btw, the F-17 was cancelled, the F-20 was never considered, the F-12 only existed on paper. There were 2 different aircraft called the A-12, one CIA (though with AF markings, and the other a cancelled Navy aircraft of a completely different type).

And yet, given all the problems they experienced with the F-4, someone still thought a one-size-fits-all aircraft was a good idea... sigh...

@HephaestusAetnaean the YF-17 became the F/A-18. It's the same plane more-or-less... YF-17 was the prototype.

@SnakeDoc - YF-17 was a prototype for the [never realized] F-17 and lost to the F-16 in the USAF LWF program. MD and Northrop then heavily modified it to become the F-18, adding 2,000 lbs to the empty weight (and another 9,000 lbs for the later Super Hornet). The YF-17 and F-18A/C look very similar, but are distinct a/c built for different services.

@HephaestusAetnaean Yes, and saying the YF-17 lost to the F-18 isn't correct... the YF-17 was revised into the F-18. The Navy had slightly different priorities in design, but the YF-17 wasn't thrown out and the F-18 done from scratch...

@SnakeDoc - Yes, and saying the YF-17 lost to the F-18 isn't correct Well, of course... the YF-17 lost the LWF competition before the F-18 even existed. Someone would have to be awful silly to make that kinda typo, dontcha think? [and of course I delete the wrong comment...]

There was no F-17. The YF-17 lost to the F-16 (only 2 built). The F-22 and YF-23 both had proposed naval variants. Neither left the drawing board though. If the F-20 and "F"-23 make that list though, you may as well include the "F"-32 and naval F-111B.

Here is a list of ALL U.S. Fighter Aircraft, in service and retired - the US made dozens more fighters, from WWII props, to early jets, to the century series.

@HephaestusAetnaean The question specifically identifies the Air Force not the Army Air Corps. The Air Force never operated a piston fighter. The list I posted, if you scroll up or down, actually includes every aircraft in service or retired, the reference in my post is about the link, not the information in this post. I did miss some aircraft though, updating now.

Your blanket USAF piston fighter claim is wrong.  The USAF separated in 1947 still early in the jet transition, and it operated F-51D's in Korea until at least 1953.

Doesn't change the answer, but that list from Wikipedia missed the fact that the USN operated F-16's as Top Gun adversary aircraft. According to a friend who flew them, they were the best-performing F-16's because they were optimized for air-to-air and left off equipment (i.e. weight) that was only used for air-to-ground.

Maybe not technically a fighter, but the A-1 Skyraider was (in different variants, like the F-4) also used by all services.
It was even used in air to air combat, shooting down at least one North Korean and one Chinese aircraft during the Korean war and several North Vietnamese MiGs during the Vietnam war.
Not sure if that makes it a fighter according to whatever definition you're using.

The FJ Fury is actually a Navy/Marine derivative of the Air Force F-86 Sabre.
Variants of the Northrup F-5 were also used by all services, although mostly in adversary training roles. The A-7 was used by the Navy and Air Force, but I don't think the Marines ever flew them (fighter?).
And going back further, and in the non-fighter category, the B-24 had a Navy variant in the PB4Y--not Marines again.

A-7 was indeed never used by the Marines. They stayed with the A-1 longer in the close air support role, and A-6 and F-4 variants for bombing missions.


text:
What does it mean exactly when an aircraft is "35% unstable"? (aircraft stability factor)
CNN's Grumman X-29: The impossible fighter jet with inverted wings contains several interesting photos, and says:

It was unflyable -- literally -- without a digital flight computer on board, which made corrections to the flight path 40 times a second," said Christian Gelzer, chief historian at the NASA Armstrong Flight Research Center in southern California (where the plane was tested) in a phone interview.

"An F-18 fighter jet has an instability factor of only 5%. The X-29, on the other hand, was 35% unstable," said Gelzer.

Question: What is the "aircraft stability factor" and what does it mean exactly when an aircraft is "35% unstable"?

The Grumman X-29 had a wingspan of 27 feet and was 48 feet long. It could reach Mach 1.8 (1,100 mph). (NASA)

It's just a pessimistic way of saying it's 65% stable.  ;)

At the most fundamental level, aircraft stability is governed by the relative positions of the center of gravity and the neutral point. The neutral point being the point about which the pitching moment experienced by the aircraft is independent of the aircraft's orientation.
A useful number that quantifies the relative position of the CG and NP and allows comparisons to be made between aircraft of different size and shape is the Static Margin.
It is defined by the distance from the neutral point to the center of gravity normalized by the mean aerodynamic chord.
$$ \text{Static Margin} = \frac{x_{np} - x_{cg}}{\bar{c}} $$
In the case of the X-29, it being 35% unstable means the static margin is -35%, or the neutral point is ahead of the center of gravity by 0.35 of the mean aerodynamic chord.
What this practically means is that in a similar manner to how an inverted pendulum will fall over with the slightest perturbation, the X-29 will almost immediately tumble out of the sky without constant corrections by the flight computers.


text:
Why is a Lockheed MC-130J Commando II creating such a loud droning sound?
Today I heard a loud droning sound which is really unusual in the area of west London I live in; so I went on ADS-B exchange and it showed a USAF Lockheed MC-130J Commando II flying literally right over my house. However, it showed the altitude as being 27,000ft! I didn't know you could hear airplanes which are flying that high. Is it a case of the engines being so loud on that particular case or maybe the wind transferring the noise etc?

It could also be resonance or constructive interference in your building. My office is near a switching yard where diesel locomotives often idle. The sound resonates loudly at my desk, but is inaudible if I step a few feet away in any direction. If the plane's engines were running at just the right speed, and you were sitting in just the right place...

There are two factors reducing the volume of a sound when travelling through the air:

The pressure wave expands as the surface of a sphere, which will reduce pressure as a function of distance $r$:
$$ p(r) \sim \frac{1}{r^2} $$
Since human hearing is logarithmic, we typically use Decibels (dB) as a unit for volume, rather than pressure directly:
$$ L_p = 20 \log_{10} \left( \frac{p_\text{RMS}}{p_\text{ref}} \right) $$
This means that an aircraft that is twice as far away will (at maximum) have a sound pressure of one quarter left, which corresponds to $ 20 \log_{10}(1/4) \approx -12 \, \mathrm{dB} $. An aircraft at 27,000ft will only be $ 20 \log_{10}(1/27^2) \approx -57 \, \mathrm{dB} $ less loud compared to an aircraft on final approach at 1000ft. For a large and loud turboprop, this is easily enough to hear it, considering the engines can reach up to 140 dB and aircraft on approach are typically up 80 dB loud:

The absorption of sound waves in air is frequency dependent. This physics.stackexchange answer explains the details. The following plot shows the absorption coefficient as a function of frequency for different humidities:

(image from Wikimedia)

Since turboprops are producing more lower frequency sounds with their propellers compared to turbofans, they can be heard further (they also typically fly lower).
This also matches the "droning sound" you describe. The higher frequency noise has been absorbed by the atmosphere.

@RodrigodeAzevedo The threshold of what you can typically hear (in absence of other background noises) is 20 µP, which is the $p_\text{ref}$ in the equation above. That means you can hear anything above 0dB.

Yes, you can definitely hear planes from that altitude. Twin turboprop regionals flying over my city at altitudes between 21000 to 25000 ft are clearly audible at pretty much any weather, so a C-130 being much larger and having two more engines would have no trouble transmitting sound down to the ground from 27000 ft.

Great answer - gave the vote to the guy above though purely for the effort he put in with regard to the mathematics behind it; although yours is clearly easier to understand

No problem @Daniel K, I think Bianfable totally deserves it as his answer explains the how and the why, mine is simply a witness testimony, and as such not very informative.


text:
What is a flying fuselage aircraft (FFA)?
I'm fond of ultralight flying and stumbled over the SF-1 Archon site.
Specifications for more details.
I found it very appealing as an ultralight and feel like flying it even though i don't have any prior experience with pusher configuration.
I have never heard of the FFA (flying fuselage aircraft) concept so far. My knowledge is rather limited to basic conventional aircraft where the fuselage is considered to neutral by design.
Can someone expand on it please?

One day with SF/1 Archon video on youtube

Excerpt from a forum: "basically a Fat Ultralight, with a Rotax 503 ( about 50 hp) 2 stroke in a semi-duct with a full sized prop."

I found this off the website after some searching:

The advantages of the flying fuselage aircraft (FFA) category,
  compared to conventional aircraft (CA) category and flying body
  aircraft (FBA) category, are the following:
In conventional aircraft design, the fuselage is aerodynamically
  neutral and joins only the separate parts of the aircraft. As the
  wings grow the buoyancy grows as well. In the flying body aircrafts,
  aerodynamic lift is produced only on the outside of the fuselage and
  the wings, which comprise a unite body. As the fuselage and wings
  grow, the generated lift becomes greater. In the flying fuselage
  aircraft the extra lift is generated from the interior of the fuselage
  and from the whole aircraft in and out. Thus, maximizing the full
  extent of the aerodynamic performance of the aircraft. Practically,
  the new category of the flying fuselage has the following advantages
  compared to the other categories above. i) because of the greater
  generated lift ,the aircraft is designed smaller in size, in order to
  have the same performance as its peers.
ii) due to the smaller dimensions of the aircraft, it occupies less
  space and needs a smaller hangar. (cost reduction).
iii) the most important advantage is that during the flight in
  conventional and flying body aircrafts, stability comes only from the
  main wings dihedral, as well as the size of caudal. The flying
  fuselage design acts as a funnel and provides extra stability to the
  aircraft, making the air mass passing through the fuselage in a column
  of air (air shaft). This is maximizing the stability of the aircraft
  in all angles and phases of flight. Source

So what I think what they're trying to say is that the body generates lift as well. It sounds mostly like something like a blended wing body or lifting body in my opinion as a meeting point between a conventional and flying wing aircraft. In any case, the term FFA seems very uncommon and not widely used.
SF-1 http://www.aerosports.gr/images/photos_gallery/archonSF1/4.jpg
The closest similar thing I've found was this aircraft. The F-22 Raptor which it seems to closely mimic is not considered a flying wing nor a blended wing body, and after looking at the fuselage I remained a little unconvinced that it generates substantial lift as a body due to the substantial upper structure and lower structure.

This sounds very enthusiastic but some factual evidence would be great to support the (rather optimistic )  claims. Mind you,  seems like a fun machine!

The key seems to be "In the flying fuselage aircraft the extra lift is generated from the interior of the fuselage and from the whole aircraft in and out." - it basically implies that the whole thing is a sort of ducted fan / ducted airfoil.

indeed, ducted fun makes more sense.

@menjaraz Yes, the front picture shows two very large ducts on the sides of the fuselage. Makes me wonder about the drag...

The F-22 is definitely a blended wing-body (as are most fighter aircraft since the 1970s, for that matter).

"Flying Fuselage" is kind of a buzzword for this aircraft, as far as I know. Normally they're called Lifting Body aircraft. The point is to make the fuselage generate lift by shaping it somewhat like a wing. The ones on the wiki page generate 75% or more of their lift with the fuselage alone, but they don't have to; for example, the Piaggio Avanti's fuselage generates a good bit of lift, allowing its wings to be shorter. An example on the extreme opposite side would be the Apollo crew capsules. If necessary, they could be angled in such a way that the capsule produced lift while it flew through the extreme upper atmosphere. This allowed them to adjust their re-entry trajectory without having to carry fuel or wings.

I'm afraid, it has nothing to do with lifting body aircraft. I know of the Facetmobile (powered with a rotax 503) and i am firmly convinced that a lifting body ultralight should look alike


text:
Is there a more specific term than 'flight line' for straight lines flown during flight?
I work for a small software startup, where its just my boss and I. Prior to this job, I had no experience with aircraft. We have a client that uses our software to fly a pattern over an area, where they fly straight for a while, turn around, and fly back over an adjacent area. They do this so that they can canvas an entire area. I sketched out what this looks like below.
      (start) ---------------------> (turn around)
                                    )
(turn around) <---------------------
             (
              ---------------------> (turn around)
                                    )
(turn around) <---------------------
             (
              ------------>    (and so on)

My boss refers to one of these straight flights as a "flight line". When I looked up the term "flight line" though, I found that it has a few different meanings all related to where the aircraft is parked or serviced on the ground.
So my question: Is there a more correct term than "flight line" that describes the patterns our client flies, which are these sets of straight lines?

related: Why did this aircraft fly in this pattern over Southern Italy?

Do you know what the customer calls it? Or can you ask? The pattern is specific to surveying, so it only has a name in that specific domain.

Although my aviation knowledge is not all encompassing, I would argue that you, your boss, and your software company may want to know your audience as well as possible. The same terminology can mean different things to different segments of society. For instance, uncontrolled airspace/airfield would mean something totally different to a pilot than it would mean to the media or general public.
A quick search of the Federal Aviation Regulations/Airmen’s Information Manual, the Pilots Handbook of Aeronautical Knowledge , and the Airplane Flying Handbook only garners results describing specific areas of an airfield and the personnel working there. My experience in civilian aviation and in the military is consistent with this usage. When pilots, ATC, and others in the aviation field describe an aircrafts path, they use terms such as the following:

Route
Return route
Round-robin route
Great circle route
Flight path
Leg
Direct leg
Course
Direct course
Track

The term you are probably looking for is Transect pattern consisting of transect lines.
Someone more knowledgeable might have a better term.

Nothing technically incorrect with this answer, but for a software guy who admits to having little aviation knowledge, do you think mentioning (but not defining) great circle route does anything to answer the specific question or enhance his understanding?  And when have you ever heard a pilot say that they were flying a “transect line”?

I appreciate all the terms you listed! In all fairness, my boss is pretty damn smart / knowledgeable; he definitely knows his audience. I was just wondering on my own if there was a better term.

Definitely not "flight line" though!  In fact it is a timeworn joke on newbies to ask them to get you a bucket of prop wash and 10 feet of flight line.  Your boss's credibility will definitely take a hit if he sticks to that term!

@MichaelHall I once heard a story of a clever boot involving a request for 100 yards of flight line, an old Seabee storehouse, Marston mats, and a forklift.

The correct term is a Route Segment. CFR 14 part 1 describes a Route Segment as

a portion of a route bounded on each end by a fix or navigation aid (NAVAID).

If the flight is in a straight line from one point to the next, it is said to be "Direct". From a common usage standpoint, DJClayworth is correct in that a "leg" is used to describe a section of a route. However, a leg may contain multiple waypoints or, from a commercial operator's standpoint, an entire flight between airports.
I am unaware of a standard aviation term for the multiple parallel segments, but as the operation in a type of survey, I think Dan F.'s "transect" description is appropriate.
The term "Flight Line" is only used, to my knowledge, to refer to the parking and servicing portion of the airfield apron.
The term "Flying the Line" is often used to describe a pilot or crew which is actively and frequently scheduled to fly the unit's or company's sorties.
Hope this helps. (Current Active Duty USAF pilot flying for 20 years)
Addition - I have worked with units and contractors whose mission was ground mapping and sensing using airborne LIDAR (Light Distance and Ranging). Their sortie profiles were very similar to the one you described. The USDA published guidance for data collection from aerial LIDAR platforms (https://www.fs.fed.us/pnw/pubs/pnw_gtr768.pdf). I have posted their graphic with their names for the various patterns.

Welcome to [Aviation.se]! I've edited your answer a bit to make it more readable and to use quote formatting for the quote. Thank you for serving our country!

The straight legs of a search grid pattern are not bounded by navaids.  Also, you said that the correct term was route segment, then later agreed that transect is appropriate.  (I know, i used two similar yet different terms in my answer too!)

Thanks for the assist FreeMan.

Michael Hall - Yes, the original question is a hard one to answer comprehensively. That said, a route segment can be bounded by a fix or NAVAID. A fix can be described by a visual reference point, a NAVAID radial/DME or radial/radial intersection, a standard RNAV (Area Navigation) or DAFIF (Digital Aeronautical Flight Information File) point, or any other reference which can be use to identify a specific location. The straight portions between fixes are route segments, but the overall pattern of parallel segments doesn't have a standard aviation name that I know of.

In the world of idealized navigation, a journey consists of flying a straight line from your departure point to another location, making a turn and flying a straight line to a different point, and so on until you reach the point that is your destination. Reality is a bit more complicated, but it's a useful approximation.
The points are called "waypoints" and the straight lines are called "legs". Although your flight path is a bit different from this, the term "leg" might well apply.

Leg is not a bad term, but I think it’s more appropriate to a cross country flight like you describe.  Just an opinion though...

I'd think "LEG" is a good term. It matches up with what each straight segment is called in a Flight Management System.

At least in airline terminology a ‘leg’ is take-off to next landing, as a ‘flight’ might have intermediate landings.

The term leg matches with general non-aircraft navigation as well.

Without delving into too much detail, the most appropriate pilot terms for the straight legs of the search grid you describe would be “track”, or “course”.  Both terms are essentially interchangeable, and are often modified to “ground track” and “true/magnetic course” for clarity.

These describe the direction you are flying, not the act of flying straight for a while.

Yes, you normally have to fly straight for a while to maintain a direction.  (With minor adjustments for wind on longer segments)

From the description of your situation, I would call the entire pattern a "grid sweep" and reffer to each line as a "grid line".
Gotta mention I have nothing to do with aviation :)

I have little knowledge of aviation but the idea reminds me of scanlines as they are used in computer graphics as described here:
https://en.wikipedia.org/wiki/Scanline_rendering
Maybe scanline is a more appropriate term.

Welcome to Av.SE. Good brainstorming idea!

Interesting answer.  I have little knowledge of computer graphics, so I would probably avoid going on a computer graphics Q&A board and propose using aviation terms.  But that’s just me...


text:
At what position or distance from an airport are you considered to be in the "traffic pattern"

image source

In the United States, as an aircraft is approaching or departing a
non-towered airport, at what position or distance from the airport
are you considered to be in or out of the "traffic pattern".
Is it different for an airport with a operating tower?
Does it vary with other countries?

Hint: a regulation exists but it is not in part 61 or 91 (think, space shuttle)...

FAR 157.2 for airport planning states, "Traffic pattern means the traffic flow that is prescribed for aircraft landing or taking off from an airport, including departure and arrival procedures utilized within a 5-mile radius of the airport for ingress, egress, and noise abatement."
In other words, once you are within the airport operation area, you are part of the "traffic pattern". The airport operation area is 5 statute miles unless otherwise noted and therefore makes no difference whether a control tower is operating.

Why would it be statute miles?

This AC describes a fair bit of what/where a traffic pattern is. ultimately it comes down to definition but the answer seems to be what ever the defined traffic pattern says

The airport traffic patterns described in part 93 relate primarily to
  those airports where there is a need for unique traffic pattern
  procedures not provided for in part 91. Part 97 addresses instrument
  approach procedures (IAP). At airports without operating control
  towers, part 91 requires only that pilots of airplanes approaching to
  land make all turns to the left, unless light signals or visual
  markings indicate that turns should be made to the right

It seems they are somewhat careful to not explicitly define anything and instead allow some definitions to define it for explicit cases and others to be left to interpretations. The FAA advises that calls be made as far as 10 miles out.
The FAA technically allows airports to define their traffic pattern themselves:

Traffic Pattern Design. Airport owners and operators, in coordination
  with the FAA, are responsible for establishing traffic patterns. The
  FAA encourages airport owners and operators to establish traffic
  patterns as recommended in this AC. Further, left traffic patterns
  should be established, except where obstacles, terrain, and
  noise-sensitive areas dictate otherwise

They do provide some guidance on how to do so in regards to altitude they even allow the pilot to decide

Traffic Pattern Altitudes. It is recommended that airplanes observe a
  1,000 foot above ground level (AGL) traffic pattern altitude. Large
  and turbine-powered airplanes should enter the traffic pattern at an
  altitude of 1,500 feet AGL or 500 feet above the established pattern
  altitude. Ultralight aircraft should operate no higher than 500 feet
  below the powered aircraft pattern altitude. A pilot may vary the size
  of the traffic pattern depending on the aircraft’s performance
  characteristics

Going straight to regulations taken from here

§91.127   Operating on or in the vicinity of an airport in Class E airspace.
(b) Departures. Each pilot of an aircraft must comply with
  any traffic patterns established for that airport in part 93 of this
  chapter.

and for class D

§91.129   Operations in Class D airspace.
(1) Unless required by the applicable distance-from-cloud criteria, each pilot operating a
  large or turbine-powered airplane must enter the traffic pattern at an
  altitude of at least 1,500 feet above the elevation of the airport and
  maintain at least 1,500 feet until further descent is required for a
  safe landing.

and Class C

§91.130   Operations in Class C airspace.
(b) Traffic patterns. No person may take off or land an aircraft at a satellite airport within
  a Class C airspace area except in compliance with FAA arrival and
  departure traffic patterns.

If the tower is in operation they can vector you as they see fit (at least here under the FAA) as such they may use pattern terms and organization but I cant tell if the FAA considers it a pattern or not if there is a tower.


text:
What is the purpose of these odd "control surfaces" on the BAE Taranis?
I was looking at a video of the BAE Taranis, and noticed these weird control surfaces:

There is a matching pair on the underside. They don't seem to move at all throughout the video, even on landing, and yet they seem to be slightly extended.
What are they?

No citation for this, but they are a variant of the bleed air system on the Harrier and F-35 for control during hover, except here its for use during normal flight - its used here to cut down on moving surfaces which harm the stealth characteristics.

@Moo they look an awful lot like spoilers if you ask me

They look like spoilers but are more precisely called drag rudders. They are not meant to reduce lift like regular spoilers, but increase drag in order to create a yawing moment.
Regular aircraft have a vertical tail for yaw control. Without this, you need some force acting at a lateral distance from the center of gravity for yaw control, and this is what these speed brakes do. They are opened only on one side, and keeping both slightly open increases control power because then one can be closed while the other can be opened further.
The Northrop B-2 uses split ailerons to the same effect, and the Horten IX had a two-stage wooden speedbrake which could be extended near the wingtips. By raising only the smaller brake with small rudder pedal movements, yaw control could be tailored to flight speed. At high speed only small input was needed, and at low speed both brakes could be fully opened for maximum yaw control.

Horten IX V2 3-side view (picture source). Note the two extended speed brakes near the wingtip in the front view. The real speed brakes were on the lower side of the center wing and right behind the rear landing gear bay (in the drawing called spoilers).
Thanks to @RedGrittyBrick for the hint: Yes, the X-47A and X-47B also seem to have drag rudders. I guess their large chordwise dimension helps to limit the lift loss when they are extended.

Northrop-Grumman X-47B in flight (picture source)

It looks like the X-47A and X-47B may have similar control surfaces.

At a first glance, most likely differential spoilers to facilitate yaw control, as there is no vertical fin.  The B-2 Spirit stealth bomber uses a similar arrangement with a differential spoilerons on the wingtips for yaw authority.

authors: یداله یداله زاهدی منش


text:
Why should a test flight be performed when the propellers are changed?
From this question I've learned that after a propeller change the plane should go through a test flight. Why is this?

A test flight must be done anytime after maintenance, preventive maintenance, rebuilding, or alteration this is not exclusive to propellor change or overhaul but just about any major and most minor work.

A test flight must be done anytime after maintenance, preventive maintenance, rebuilding, or alteration  <-- This is not strictly true: It's certainly good practice, but not a regulatory requirement (at least under FAA regulations - Greg cited the relevant FAR below).

Is a propeller change a failure / error prone operation?

Does a prop change actually require a test flight, or simply a runup?

The purpose of the test flight is for the safety of passengers. For most maintenance, in a not-for-hire aircraft, a private pilot can perform the test flight and determine the aircraft is airworthy, but they must do it without passengers.
Title 14 chapter 91.407

It should go without saying that replacing the propeller may have "appreciably changed [the aircraft's] flight characteristics or substantially affected its operation in flight"

@voretaq7 I'm not so sure that "goes without saying". Today's manufacturing techniques are very good at exactly replicating items to very tight tolerances. It's reasonable to expect a routinely manufactured item like a plane propeller to be exactly like the previously used one (and therefore a safe item to swap at will).

If you replace breaks on a car the car breaks differently then it has been for the last few months. Why should a new prop be identical to the one your replacing. If that were true you wouldn't need to replace it. If it's not identical then "something" changed.

@coteyr What I was getting at, is that this change does not intuitively mean different flight characteristics to a non-aviator. After a brake change, most people wouldn't automatically classify their car as "unsafe for passengers" until they've tested it.

@SnakeDoc It doesn't matter how perfectly you replicate something, it still needs to be physically installed on the aircraft - an error-prone process. Installing new flight control surfaces doesn't intuitively mean different flight characteristics to a non-aviator either (and for that matter some aviators might think it's no big deal - they're identical to the old ones, right?).  Any mechanic will tell you it can seriously change flight characteristics though - especially if there's a problem in the reassembly.

@voretaq7 That's a great clarification and explanation. It should be added to this answer if possible, as it fully answers the "Why" in the OP's question.

@voretaq7 It's interesting that a commercial airliner can have an engine removed from it, completely tear it apart, replace or repair components inside of it, put it back together, mount it back to the airplane, inspect it, and then just do a ground run before they load it up with hundreds of passengers to go fly without a test flight, yet a lowly propeller replacement needs one? Keep in mind that an aircraft has to be released from maintenance and be airworthy before it can fly, even for the "operational check flight (flight required by 91.407)" which may or may not even be required.

It is actually false that the pilot determines that it is airworthy by during the test flight. The aircraft must be airworthy before you ever take it up in the first place, otherwise it cannot be returned to service as required by 91.407(a).

@Lnafziger You can do a full-power ground run for a replacement propeller (or engine) in lieu of the test flight , and you could probably get away with just a ground check of the flight controls too per 91.407 (c). The question is do you (and the mechanic) feel that the repair or alteration can be adequately tested on the ground: For a propeller change a ground run will verify it won't fall off (which is important), but we know it can affect performance (if you're replacing a worn propeller with a new "perfect" airfoil), which is something most of us can't easily test on the ground.

@voretaq7 If it is a "new perfect" prop which conforms to the airworthiness standards, and the ground test is good, then why would you need to fly it?  What I described above is far more involved than a prop change. (Note that I'm not saying that it might not be a good idea, but is it required?

Often when people talk about propellers, they think of them as a solid piece of material attached to the crankshaft of an engine. This is true for small planes, but absolutely untrue for larger aircraft.On small aircraft, you might do a test flight to insure that the propeller functions properly in all flight modes. Mostly you'd be looking to insure that replacing the prop actually fixed the problem your were having. Defects in a fixed prop might make it vibrate due to not being properly balanced, which will show up on runup, or it might have an internal flaw that will only be apparent at particular flight modes, like ascending, descending or level flight and turns.On larger aircraft, propellers are more sophisticated.A reciprocating engine tends to develop maximum power in the 2200 to 2500 RPM range, so the engines are set to run in this range and the actual thrust is modified by changing the angle of attack of the propeller blades. This is usually accomplished by either an electric motor or a hydraulic piston. The motor or piston is in the hub and geared to the blades.This makes the overall propeller system much more complex, and requires exercising it before certifying it flight ready even more important.Adjustable propeller blades can be turned to a negative angle to allow engine braking on landing, and backing up on the ground. It can also be 'feathered' if there is an engine failure, so that the engine will not continue to turn over if it is shut down in flight.Additional notes:There are other adjustable propeller systems that use air pressure or mechanical gearing.Gas turbine engines have an even narrower maximum power range, and require even more complex propeller systems. They turn at around 10,000 RPM and use a gearbox to turn the props in the 2200 rpm range.During my time in the Air Force, I changed propellers on C-124s, C-130s, C-133s, and a few other propeller driven aircraft. None of these changes required an actual flight verification, but did require a runup with a checklist for specific verification. Of course the pilots and flight engineer would be aware that the prop had been changed.

It is so that the props are tested to see if they have any defects or not as well as to make adjustments based on their behaviour.


text:
Can a helicopter carry a large airplane?
I saw on YouTube a helicopter carrying an airplane.
Is this possible, I mean is the maximum load compatible with the mass of this aircraft?

Related: http://aviation.stackexchange.com/questions/14334/are-there-items-bigger-than-an-aircraft-section-transported-by-air-today/14339#14339

So you claim that every video and photo of a helicopter lifting an aircraft is a fake?

"Here is video evidence of thing X. Is X possible?" Um

Begs the question if a large airplane can carry a helicopter

@wingleader Sure: a C-5 Galaxy can carry six Apaches, according to Wikipedia. (Pet peeve: you mean that it raises the question; to beg the question is to assume the answer. For example, asking whether a helicopter can carry a plane begs the question of whether helicopters even exist, since the question makes no sense without assuming that helicopters exist.)

This airplane carries about 80 passengers, so it's actually quite small plane, compared to B747 with 400 people. And in general "can X carry Y" the answer is always "Yes, provided sufficiently big X paired with sufficiently small Y".

If you look more closely, this "airplane" is only the husk of a Tupolev Tu-134, a rather small airliner, and the helicopter is a Mil-26, the heaviest helicopter ever to go into production. Not only are the empennage and the outer wings missing, but also the engines, which helps to reduce the load considerably.

Mil-26 lifting a Tu-134 carcass, seen from below (source)
The empty weight of a flightworthy Tu-134 is 28 tons, but the engines alone weigh 2.3 tons each. Now remove the outer wing, empennage and cabin interior, and the remaining weight is within the 20 ton load limit of the Mil-26.

I guess "Very powerful heavy lift helicopter lifting half of a stripped down actually-not-that-big airplane" just doesn't have that ring to it …

One of the purposes of the Sikorsky CH-54 was to transport aircraft.

Carrying a Chinook:

Lifting a Caribou:

Yo dawg, I hear you like helicopters, so I put a helicopter under your helicopter so you can lift while you lift.

In Vietnam it was pretty common to remove crashed aircraft from the jungle using helicopters.
http://www.angelfire.com/mo/242sdASHC/213th.html gives a first hand account of a crewman flying quite a few of these dangerous missions.
http://www.combatreform.org/CH53AliftsA1andA4.jpg shows an A-1 and an A-4 being lifted by CH-53s, but larger aircraft like F-4s and F-105s were similarly airlifted out of the jungle to prevent them from falling into enemy hands.


text:
Do airline pilots ever risk not hearing communication directed to them specifically, from traffic controllers?
I gather pilots communicate regularly with air traffic controllers within air traffic controllers' jurisdiction or airspace as they enter the space, during their time in that space and as they leave.  In some or most instances, they will not land in that air space, they are simply passing through and may encounter lots and lots of regional and international air traffic.
They are routinely directed by air traffic controllers to fly at a certain direction, increase or decrease altitude for safety in order to avoid collisions and accidents.  In most instances, auto pilot is engaged and I assume the headphones come off, for flights longer than say 2 hours or even 1 hour.
Speaker phone may be on but pilots can read a book or watch a movie on their laptop or revise their reading on knowledge of their ever changing craft.  At a certain frequency.
I gather lots of communication to planes occurs and listening to all of them can become tedious and may require too much concentration.  In this light, do airline pilots ever risk not hearing communication directed to them specifically, from traffic controllers of space they are flying past on cruise?
Does a light or sound or siren switch on when a message is directed at them and I assume they differentiate communication directed at them by their call sign, e.g., American Airlines Flight 200.
Is there a risk they might not hear it and how is that risk mitigated?

See https://en.wikipedia.org/wiki/SELCAL

Pilots are not allowed to do any of the things you mention. Basically all they can do in the cockpit during cruise is watch the instruments, do flight related stuff (communicating, looking up procedures they'll need next and briefing them and similar), and make small talk. Definitely no book reading or using tablet except as electronic flight bag. They can eat though, and of course they sometimes need to go to the restroom.

(and note I didn't include fly the plane, because in RVSM space, i.e. above FL290 where most airline flights cruise, using autopilot for altitude hold is required—pilots often do hand-fly approaches and departures, but nobody hand-flies in cruise (in an airliner))

One of the reasons why pilots aren't allowed to do any of those other things: https://en.wikipedia.org/wiki/Northwest_Airlines_Flight_188 (although it wasn't allowed at that time either, and yet it happened).

@JanHudec according to this answer the PNF is allowed to sleep - he's not allowed to do anything else?

Update:  9th of April a Tui 737 was intercepted over Montenegro due to a loss of comms   http://www.avherald.com/h?article=4c682389&opt=0

There is a ton of radio communication during the taxi, takeoff and departure phases, and then again during the arrival, landing and taxi phases. Pilots are generally very busy at these times and 100% focused. Airlines have two pilots, and one will be flying while the other works the radios and monitors various instruments.
Cruise is another matter. There generally isn't a lot to do other than keep an eye on the autopilot. The pilots will take turns eating, resting, going to the lav, etc. Radio work usually involves little more than getting handed from one frequency to the next. They may get rerouted due to traffic or weather, but it only takes a few seconds to update the autopilot.
Either way, pilots do occasionally miss radio calls. So does ATC for that matter. It's common enough that nobody gets worried about once or twice, though it's annoying. If it's a real radio problem, there are procedures for both sides to follow to keep everyone safe.
There (usually) isn't any sort of light or tone when someone is calling you. However, the standard format is "called station, calling station, message", so with a little training, your brain can quickly tell whether the message is for you. If so, it "tunes in" and you consciously hear the message; if not, it "tunes out" and the message is just background noise.

"There isn't any sort of light or tone when someone is calling you. " - well, there is SELCAL, which is exactly that - but it isn't usually used in domestic operations.

@pericynthion: Why not?

@Sean because SELCAL is primarily (perhaps only) used on HF frequencies, which are used over oceanic or other very remote regions where there is no VHF coverage. The audio quality of HF is much worse than VHF, and there's no squelch, so SELCAL relieves the pilots of the need to listen to squealing static for hours on end trying to pick out their callsign.

When a pilot is given instructions, clearances etc. from a controller, the pilot has to acknowledge they've heard it and certain items need to be read back to the controller.  If the controller doesn't hear anything they will repeat their message and keep trying to contact the aircraft.  The rules for UK readbacks are included in a CAA document CAP413, along with other conventions and standards for communication between flight radio telephony stations
It's not that uncommon, these days, for fighter aircraft to be scrambled to intercept unresponsive aircraft
There is less communication that you'd expect once you've made contact with a controller and been given your clearances.  It isn't an onerous task to listen in to all the chat and respond when you hear your callsign

Normally pilots do not communicate much with ATCC between airports. For example, in small aircraft normally the pilot will often hear nothing from ATCC unless they have specifically requested flight following. Small VFR aircraft usually fly with a 1200 transponder code which is generic, and in that case it is tricky for an ATCC to even contact the plane at all.
For larger aircraft, usually a separation is guaranteed from instructions at the beginning of flight and contact is only necessary if something changes, so your guess that they talk to the pilots "regularly" is not really correct.
Note that most commercial aircraft monitor 121.5 in addition to their assigned frequency and an ATCC will always try that if they are getting no response on an assigned frequency. So, big planes have to screw up twice to go incommunicado completely.
If an aircraft is unresponsive, then what happens depends on a lot of different factors. The bigger the aircraft, the more actively ATC will react. If it is a small aircraft on IFR, then ATC will assume the pilot is on the wrong frequency and just steer other aircraft around them. If that causes a big problem, the offending pilot will get written up. Usually the pilot will figure out he is out of contact once he gets closer to civilization. If it is a heavy, ATC will make repeated attempts to contact and do the same thing as with a smaller plane: steer others around them. If the heavy is unresponsive and deviates from its flight plan or remains unresponsive for a long time, then fighter aircraft will be scrambled to intercept and observe them. Obviously, if a commercial crew with a lot of passengers goes unresponsive for so long that it requires an intercept, they are going to get in trouble. By "they" I mean the captain and first officer.

So in essence pilots are assigned a certain frequency and its unique to each plane , also unique to each fight, so the momen they hear the radio, they know its directed to them and no one else and hence they respond

@securitydude5 No.  There is a common frequency for the controlling station (there may be more than one frequency if there's a lot of traffic).  All the appropriate traffic will be on that channel.  For example Shannon Approach is 121.400 and everyone flying into Shannon will be on that - you can listen in at  https://www.liveatc.net/search/?icao=einn

SO I guess pilots use SELCAL then or so they do not devote all their time to radio listening, perhaps some do some dont?  What is the standard?

@securitydude5 When ATC wants to talk to an aircraft they use an assigned frequency (which is usually one of only one, two or three possibilities that are specific for that center or tower). They address the plane by using its call sign. For a commercial aircraft the call sign usually has their flight number. For example, "Contact Boston Center on 129.1, United One Seven Six Zero".

@securitydude5 - It's not a good idea to select out other radio calls, they can tell you where other traffic is, what it is and where it's going.  Actively listening to other aircraft is encouraged to increase situational awareness

@securitydude5 One of the skills pilots pick up is the ability to pick out their call sign in the background of radio chatter, just like you can notice when someone's saying your name in a crowded room.

Adding to what @DaveGremlin wrote above, even when I am technically not flying as a pilot, in GA, I'll usually pester the pilot before takeoff to let me listen in to the radio chatter. That has several advantages; e.g., (a) it reduces the risk that we miss an important radio call; (b) it helps if there is uncertainty about critical information such as squawk codes; (c) it helps maintain situational awareness for both of us; and (d) it reduces the risk of me talking to the pilot on top of a radio call. Plus a side benefit: for someone not often flying in controlled airspace, it's good practice.


text:
Why does the N1 on a FJ 44-2A turbofan go to 104.4%?
Whilst watching a video of a Beechcraft Premier A1 Jet whilst in the cruise at FL330 I noticed the N1 on both engines were at 104.4%.
Can anyone explain why they can go over 100%?

related, if not a dupe.

this answer explain what 100% actually designate (for another engine).

100% is the designed speed - sometimes it can be proven, that slightly more is still safe to operate on. Now: Change all scales, so that the new full power is once again 100% - or allow more than 100% on the scale? As a matter of fact, this is much easier to do, as the software does not have to be changed a lot, dependencies to other components are still valid, the recertification mostly is also easier, ... This also has been done for the Space Shuttle Main engines, routinely operating at >100% nominal ( = design) thrust.

100% isn't a design limit.  It's not any kind of limit.  Engine RPM's in turbine engines are quite high; the percentage is just a reference number, and nothing more.
Different components of turbine engines operate at different speeds: a compressor section vs. the power section and fan, for example.  Different names or terms are given for the various speed and component values, such as N1, N2, Ng, etc.  Each will have their own speed limits, but in all cases, 100% has nothing at all to do with a limitation.  It's only a reference value for power management, trend recording, etc.
Actual limitations are calculated based on temperature and desired power.  Most turbine operations are conducted with a reduced power on takeoff, for extended engine life, and for safety.  A takeoff runway safety analysis takes into account airport elevation, ambient temperature, wind, slope, aircraft weight, obstacles, runway length, etc, and the takeoff power value is determined at that time.
100% does not represent 100% thrust.  Percentage of RPM does not equate to a linear change in thrust, and the higher one gets in percentage, the steeper the power curve goes: small incremental changes at high power settings produce considerably more thrust than larger changes at lower power settings.  100% N1, N2, or Ng doesn't represent a fixed thrust value, fuel flow value, temperature value, or actual power value.  It's just a reference system for that section of the engine.
Because different engine sections operate at different speeds relative to one another, one component may be operating at 100%, while another might be at a completely different value: they turn independently, and the engine parameters that count aren't so much the RPM, but the temperatures.  Only when maximum values are to be exceeded are the RPM's relevant, other than as reference numbers when setting power.